JPS5949566A - Detecting device of original density - Google Patents

Abstract

PURPOSE:To perform the picture control without the influence of the change of the quantity of original density detecting light, by using a reference density plate to compensate the change of the detection density of the original due to the change of the quantity of light. CONSTITUTION:The dynamic range of a distribution characteristics is changed by the detection density of a reference density plate 18 to change the frequency distribution, thus compensating the change of the detection density of the original due to lowering of the capacity of an original density detector 16. That is, when a back and forth moving original scanning means is moved forth, the density of the reference density plate 18 is detected, and the density of an original 19 is detected. The original 19 is placed on a platen glass 1, and the plate 18 is provided on the inside of an outside box 17 and in the position facing the detector 16 which is moved on a shaft. Consequently, even if the quantity of light for detecting the density of the original 19 is changed, the picture control is performed without any influence of this change.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a document density detection device for detecting the density of a document and controlling the copy density in a copying machine.

First, a copying machine using electrophotography will be explained. This type of copying machine is schematically constructed as shown in FIG.

The original placed on the platen glass 1 is held down by the platen cover 2, and when the copy amount button is operated in this state, the exposure light source 3 starts exposure scanning in the direction of arrow A, and the image of the original is exposed. A first mirror unit 41 with a light source 3 attached, a second mirror unit 42, a lens system 4
3. The light is guided to a photosensitive drum 5 as a photoconductive photosensitive drum by an optical system 4 comprising a mirror 44 and the like.

The photosensitive drum 5 has a photoconductive layer made of selenium or the like provided on the outer peripheral surface of a grounded metal cylinder, and rotates in the direction of arrow B in conjunction with the exposure scanning of the exposure light source 3. For example, before the image from the optical system 4 arrives,
The charged electrode 6 to which a DC high voltage of
8 is uniformly charged, and when the optical system 4 exposes and scans the document and receives an image on the photosensitive drum 5, the conductivity of the portion that receives the light becomes quotient, and the charged charge of that portion decreases. escapes into the metal cylinder, leaving a dead charge in the dark area,
As a result, an electrostatic latent image corresponding to the image of the original is formed on the surface of the photoconductive layer.

When the photosensitive drum 5 further rotates, toner from the developing device 7 is attracted to the remaining positively charged portion by electrostatic force. As a result, the toner is attracted to the portion where the positive charge remains, and a toner image is formed on the surface of the photosensitive drum 5.

When copying is completed, the paper feed roller is moved at a timing such that the leading edge of the toner image matches the copy paper in order to match the toner image on the photosensitive drum 5-1 from the selected paper feed power center in the paper feed unit 8. 1o, and the toner on the surface of the photosensitive drum 5 is transferred onto the fed copy paper by the transfer pole 9 to which a DC high voltage is applied.

Thereafter, the copy paper is separated from the photosensitive drum 5 by dividing the first separation electrode to which AC high voltage is applied, for example, and the separated copy paper is conveyed by the conveyor belt 12 with a toner image transferred to its upper surface. The toner image is fixed in a fixing device 13 having a heated fixing roller, and then delivered to a receiving mold by a paper discharge roller 14. Even if the toner image on the surface of the photosensitive drum 5 is transferred to the copy paper by the transfer pole 9, a small amount of the toner may remain, so the surface is cleaned by the cleaner 15 and used for the next copying process. . Copying of the original is performed through the above-described cycle.

Image control in a copying machine as described above is performed by installing a document density detector in the optical system 4, and detecting the document density when the optical system 4 moves forward in the direction of arrow A (preliminary scanning) by operating the copy start button. The density of the document on the platen glass 1 is detected by the device, and the process conditions such as charging, exposure, and development after the backward movement or forward movement of the optical system 4 are controlled according to the detected density. The copy paper on which the original has been copied with the appropriate density is
I'm trying to be able to do it.

By the way, when using a reflection type sensor that is self-equipped with a light emitting part and a light receiving part as the document density detector, it is necessary to use a tungsten lamp because it is necessary to obtain a predetermined absolute amount of light. There is a problem in that the amount of light decreases due to aging and deterioration. Further, the amount of light of the original density detector changes depending on its contamination, temperature change, and the like.

Therefore, if the amount of light changes or deteriorates as described above, the density detection of the original becomes inaccurate, and appropriate copy density control, that is, proper image control, becomes impossible.

The present invention has been made in view of the above, and an object of the present invention is to detect the density of an original in which image control is performed without being affected even if the amount of light for detecting the density of the original changes. To this end, the present invention uses a reference density plate to correct changes in detected density of an original due to changes in light amount.

Examples of the present invention will now be described. FIG. 2 shows one embodiment of this, in which the original density detector 16 requires special heat resistance measures near the first mirror unit 41, so the second mirror unit 42 does not require such measures. The second mirror unit 42 is provided movably in the vertical direction on the paper 11 in FIG.
Outer box 17 corresponds to the starting point of movement in the direction of arrow A.
A reference density plate 18 is disposed on a surface that is substantially the same as the surface of the platen glass 1 facing inward.

As shown in FIG. 3, the document density detector 16 is constituted by a reflective sensor using a tungsten lamp 16a as a light emitting element and a Fumet diode 16b as a light receiving element. 16c and 16d are condenser lenses.

In the above, when the second mirror unit 42 moves in the direction of arrow A, the document density detector 16 simultaneously moves in a plane direction perpendicular to the direction of arrow A, and the document density detector 16 emits light. As shown in Fig. 4, the spot a (diameter of about 1-) of the light beam is first focused on the reference concentration &1.
8 is detected, and then a part of the document 19 placed on the platen glass 1 is scanned diagonally. Then, the document density of the portion scanned by this spot la is sequentially detected.

In this case, the characters on the original 19 are energized and are drawn in parallel or perpendicular directions along the edges of the original. Therefore, if the original 19 is scanned diagonally as described above, it is certain that some By scanning the characters, the state of the image on the document 19 can be accurately detected.
? Since the document density detector 16 is located far from the exposure light source 3, if the document 19 is large, it will have to scan a part of it, but the information on the image of the document I9 will be
can be done.

The above operations can be performed by operating the copy start button.
This is performed as a preliminary scan prior to the exposure scan for copying the original, and at this time, the density information of the reference density plate 18 and the original 19 is sequentially detected and 1. Then, in the opposite direction to the arrow entry direction (
When the exposure light source 3 scans in the backward direction (backward direction) or when it moves forward again in the direction of arrow A, an exposure scanning operation for copying is performed.

When the density of the original 19 is detected as described above, the original density signal is amplified by the amplifier 20 and then converted to a digital signal by the A/D converter 21, as shown in FIG. Detection data sent to the processing section 22 and corresponding to the density values of the original are sequentially stored in the memory section 23 for each density value, thereby obtaining density frequency distribution characteristics as shown in FIG. Note that here, the characteristic indicated by the broken line is the actual frequency distribution characteristic, but the data processing unit 22
The above is saturated. Then, the data processing section 22 detects the lowest density DI and the highest density D2 of this frequency m.

On the other hand, the document density detector 16 detects the density of the reference density plate 18 before detecting the density of the document 19, and sets the background reference density Do<FIG. 7).

By the way, when the reference density Do' of the background is set to a constant value, even when the detected original density value is detected to be lighter than the reference density Do' of the background at time T+ in FIG. 5, that is, at the initial stage, There is a problem in that, due to subsequent changes over time such as a decrease in light intensity of the original density detector 16, the original detected density value is detected as darker than the reference density Do' of the background at time T2. That is, the fifth
As shown by the solid line in the figure, the detected density value of the original changes to a darker value over time due to changes in the original density detector 16 over time, and if the reference density value is kept constant, the relationship with this value becomes out of order. Therefore, even though the originals have the same density, at time T2, the reference density of the background at time T1 is no longer D.
The relative relationship between the curve and the frequency distribution characteristic curve is different. Therefore, the same process condition control is not performed.

However, in this embodiment, as described above, the density of the reference density plate 18 as well as the density of the original are detected by the same original density detector 16.
Since the detection is performed under the same conditions, concentration detector 1
6 decreases over time, the detection reference density value of the reference density plate 18 is reached.

Also, the density becomes darker over time, except for the curve with the same ratio as the original density value.

Therefore, by using the detection reference density value Do as the reference density of the background, the original density value becomes higher than the reference density Do of the background by the same ratio at both times T+ and T2.

That is, the reference density Do of the background of the characteristic curve shown in FIG.
corresponds to the decline in the performance of the document density detector 16, and moves to the right in the figure, where the density is higher. Therefore, the original density detector 1
Despite the deterioration in the performance of No. 6, the relative relationship between the background reference density Do and the characteristic curve remains unchanged.

When the frequency distribution shown in FIG. 7 is obtained, the lowest density D1 is set as the background density, and the highest density D2 is set as the image (character) density, and the process control unit 24 sets the exposure amount by voltage control of the exposure light source 3. Copying process conditions are controlled, such as developing bias control by controlling the voltage applied to the sleeve of the developing device 7, and exposure control by controlling the aperture of the lens of the optical system.

Here, an example of a specific method for controlling image density by detecting the density of a document will be described. When H is a certain value, (a), Do < D + . . . Original with a dark background (bl, Do > DI, 1D2 DI
l > II...The background is pale and the contrast quotient (cl, Do > DI, l D'2 DI 1
<II...The background is pale and the contrast I-low, so in the case of (al), the exposure amount is increased and/or the developing bias asumi pressure is controlled to be high to lower the copy density. ), the normal exposure amount and iA image bias voltage are used, and (in the case of C1, the exposure amount and/or developing bias voltage is controlled to be low to increase the copy density. The change in the detected density of the original due to the deterioration of the performance of the detector 16 was corrected by changing the background f-density Do. Although it is sufficient to keep the relationship constant, depending on the detected concentration of the reference concentration plate 18, the frequency distribution can be changed by changing the range of the distribution characteristics described above. Even if the frequency distribution is changed so that it becomes lighter at the same rate (toward the left in FIG. 7), the original density detector 16
It is possible to correct changes in the detected density of the original due to poor performance.

As described above, the document density detection device according to the present invention has T
In a copying machine which has a document scanning means that moves back and forth relative to the document for scanning exposure of the document, and which detects the density of the document and controls the copy density, a reference density plate and a reference density plate are provided. 2. A detector for detecting the density of the original document during the forward movement of the document scanning means, such that the density of the reference density plate is detected by the detector at the start of forward movement during the forward movement. This is what I did.

For this reason, the performance of the document density detection means may change over time, or
Another feature is that even if it deteriorates due to pollution or temperature, it can compensate for it and achieve an appropriate copy density.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a copying machine, FIG. 2 is a sectional view of the peripheral portion of a document density detection device according to an embodiment of the present invention, and FIG. 3 is a sectional view of the document density detector portion of the same device. Figure 4 is a partial plan view of the copying machine for explaining spot movement for document density detection, Figure 5 is a density detection characteristic diagram, Figure 6 is a diagram of the control circuit, and Figure 7 is density frequency distribution characteristic. It is a diagram. ■...Platen glass, 3...Light source for exposure, 4...
...Optical system, 16...Document density detector, 17...Outer box, 18...Reference density plate, 19...Document. Patent applicant Konishiroku Photo Industry Co., Ltd. No. 20 Figure 4 Figure 5 Figure 6 LooD2

Claims (1)

[Claims] (1) A copying machine having a document scanning means that moves back and forth relative to the document for scanning exposure of the document, and which detects the density of the document and controls the copy density, The apparatus further comprises a reference density plate and a detector for detecting the density of the original when the original scanning means moves forward, and the density of the reference density plate is detected by the detector at the start of the forward movement during the forward movement. A document density detection device characterized in that: